"Mongooses were put on islands to help control rats, but they started eating birds and bird nests. There are so many examples. The intent is honorable, but we know by experience that it is safer to keep a species in its natural habitat."

In the face of global warming, Dr. Berger said, some of the world's species have been moving themselves.

"The caribou, for example, which used to be in Michigan, Idaho and New England, is no longer there," he said. "Any of these northern-adapted species are going to suffer as we continue to warm up across the southern tiers of their range." C. CLAIBORNE RAY